Method and system for eye-tracker calibration

ABSTRACT

The invention is related to a method and system for calibrating an eye tracking device configured to track a gaze point of a user on a display The method comprises: presenting a video on the display to a user, the video having a start size and a start position; tracking the gaze of the user, using an image sensor of the eye tracking device; and sequentially completing, for at least one calibration position, the steps of: resizing the video to a calibration size, wherein the calibration size is smaller than the start size, and translating the video to a calibration position; recording calibration data, using the eye tracking device, for the user viewing the video in the calibration position; and resizing the video to a second size that is greater than the start size.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Swedish Application No. 2150401-4,filed Mar. 31, 2021; the content of which is hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a method for calibrating an eyetracking device, and to an eye tracking system.

BACKGROUND ART

In order to perform eye tracking operations or research, it is often atfirst necessary to perform a calibration process with a user. Thesecalibration processes are executed by asking the user to dwell on aparticular position relative to an image sensor of the eye trackingsystem. One or more calibration points or calibration positions can beused to generate a gaze estimation function that is able to transform animage of the eyes, as seen by the image sensor, to a gaze direction, andtherefore to a position on a display. In general, a larger number ofcalibration points will yield a gaze estimation function with betteraccuracy in gaze estimation across the field of view of the user. Insome examples, the calibration operates by using the gaze estimationmodel to estimate a number of different parameters in an eye model ofthe user. The eye model can then be used to determine the gaze directionduring further operation of the gaze tracking device.

However, this form of calibration only works on a willing andunderstanding participant, as it is necessary to know that the user islooking at each calibration point. If the user is looking at a differentpoint, the calibration accuracy will suffer as a result. This is of aparticular issue with children and animals, such as non-human primates,as it may not be possible to effectively communicate the calibrationprocess with them or they may be uncooperative. There may also be issueswith calibration where the user lacks understanding for other reasons,such as learning difficulties, or where it is desirable to calibrate aneye tracking device without the user being specifically aware that acalibration process is being carried out.

Attempted solutions to these problems have included the use of staticimages at each designated calibration point, which are designed tocapture the attention of the user without specific instruction.Similarly, video clips can also be played at the designated calibrationpoint, on the basis that the user is likely to view them and to havetheir attention drawn to them.

Game-like calibration methods have also been proposed. Such methodsutilise a reward system. For example, a balloon may be shown at eachcalibration point and the user is rewarded for looking at the balloonduring calibration by this triggering an animation of the balloonpopping. However, this does again rely on some level of understanding ofthe user.

Another option is the use of physical calibration methods. For example,a toy may be held in a calibration target position in order to draw theattention of the user. This is of course open to inaccuracies in boththe positioning of the toy in relation to the desired calibration point,and also to the fact that the toy is likely to be larger than thecalibration target, adding inaccuracy.

It is therefore desirable to provide a calibration process thatovercomes or ameliorates the above issues.

STATEMENTS OF INVENTION

According to a first aspect, there is provided a method for calibratingan eye tracking device configured to track a gaze point of a user on adisplay, the method comprising:

-   -   presenting a video on the display to a user, the video having a        start size and a start position;    -   tracking the gaze of the user, using an image sensor of the eye        tracking device;    -   sequentially completing, for at least one calibration position,        the steps of:        -   (a) resizing the video to a calibration size, wherein the            calibration size is smaller than the start size, and            translating the video to a calibration position;        -   (b) recording calibration data, using the eye tracking            device, for the user viewing the video in the calibration            position;        -   (c) resizing the video to a second size that is greater than            the start size.

The invention therefore allows the gaze of a user to be calibrated by aneye tracking device without the specific cooperation or need forunderstanding of instructions by the user. Attention of the user isgrabbed by the video due to its content and retained due to the seamlessswitching from video display to calibration process.

The method may comprise a plurality of calibration positions, wheresteps (a) to (c) are repeated for each calibration position. The use ofmultiple calibration positions ensures that the calibration processprovides good accuracy over a whole of the display.

The second size may be the same as the start size.

The method may further comprise, in step (c), translating the video awayfrom the calibration position. The translation may be in the directionof the start position. Optionally, the translation may be back to thestart position.

The start size may be a size that fills or substantially fills thedisplay.

For example, the start size of the video may fill 100% of the display,or may fill more than 90% of the display, or may fill more than 80% ofthe display. Any area of the display not filled with the video may beempty of anything that would provide a distraction to the user. Forexample, parts of the display not filled with video may be left blank,black, filled in a single colour, and/or non-moving.

The start position may be central on the display.

Resizing and translation of the video may be performed simultaneously.By resizing and translating the video simultaneously, the attention ofthe user may be better retained on the video during the calibrationprocess.

Alternatively, resizing may follow translation or translation may followresizing.

The video may continue playing seamlessly, i.e. without breaks,throughout the calibration of one calibration point or may continueseamlessly throughout the entire calibration process. This means thatthe content of the video remains the same, e.g. a single cartoon isplayed, or an episode of a particular programme is played. Of course,the video may include scene switches or other usual features of videosduring the process, but it is preferable to avoid stoppages or lengthybreaks in the display of the video content. For example, it may bedesirable to prevent any abrupt stoppages of the video and to prevent avideo of a different genre or type replacing another video during theprocess.

By continuing the video seamlessly throughout the entire calibrationprocess, the attention of the user may be better retained. Changing thecontent of the video part way through the calibration process may risklosing the attention of the user.

Alternatively, the video may be changed part-way through the calibrationprocess. Although this may interrupt the ongoing attention of the user,utilising new content in the video may renew the user's interest in thevideo and therefore may assist with calibration of multiple calibrationpoints. In this case, it may still be desirable to provide a consistentstream of video content for each calibration point.

It may be desirable to avoid changing the content of the video whilstthe video has the attention of the user. Therefore, changing of thevideo may only occur when it has been determined, automatically ormanually, that the attention of the user is not on the video.

The content of the video may be forced to change if it is determinedthat the attention of the user has been lost. By changing the content,attention of the user may be re-captured. Detection of attention lossmay be by detecting the general gaze direction of the user, e.g. bydetecting that they have turned their head away from the display or areclearly looking to the side of the display, and may be automatic ordetermined by an operator of the system.

The video may be accompanied by audio content. The audio content may becorrelated to the video, e.g. the audio may be noises related to theactivity shown visually on the display. In some embodiments, an auditorysignal may be added to the video. Such a signal may be during the actualcalibration of a position and may make use of operant conditioning, i.e.the audio may work to implicitly train the participant to stay focusedduring the calibration event. Methods for achieving operant conditioningwill be known to those skilled in the art. By using audio and video, theuser's attention may be better retained.

The method may further comprise repeating steps (a) to (c) forcalibration points where it is determined that previously capturedcalibration data is not sufficient.

Repetition of calibration points may improve the overall calibrationprocess by removing erroneous calibration data and replacing it withaccurate calibration data.

An operator may determine that the calibration data is inaccurate notsufficient. Oversight by an operator can make sure that the calibrationdata is good enough for future eye tracking procedures. For example, ifan operator notices that the calibration data for a particularcalibration point is inaccurate or is not sufficient, they may manuallytrigger calibration data for that calibration point to be recollected.

Additionally or alternatively, an automated process may determine thatthe calibration data is inaccurate or not sufficient. The automatedprocess may be executed by the processor of the system or by anexternal, optionally remote, processor.

The method may further comprise monitoring the calibration process of aseparate display, to review calibration data during the calibrationprocess.

According to a second aspect, there is provided an eye tracking system,comprising:

-   -   a display, viewable by a user;    -   an eye tracking device, comprising an image sensor configured to        track a gaze of the user on the display; and    -   a processor, configured to present a video on the display to the        user, having a start size and a start position, and further to        sequentially cause, for at least one calibration position, the        steps of:        -   (a) resizing the video to a second size, wherein the second            size is smaller than the first size, and translate the video            to a calibration position;        -   (b) recording calibration data, using the eye tracking            device, for the user viewing the video in the calibration            position;        -   (c) resizing the video to a second size that is greater than            the start size.

The processor may be configured to repeat steps (a) to (c) for aplurality of calibration positions.

The use of multiple calibration positions ensures that the calibrationprocess provides good accuracy over a whole of the display.

The second size may be the same as the start size.

The processor may further be configured to, in step (c), translate thevideo away from the calibration position. The translation may be in thedirection of the start position. Optionally, the translation may be backto the start position.

For example, the start size of the video may fill 100% of the display,or may fill more than 90% of the display, or may fill more than 80% ofthe display. Any area of the display not filled with the video may beempty of anything that would provide a distraction to the user.

The start size may be a size that fills or substantially fills thedisplay.

The start position may be central on the display.

Resizing and translation of the video may be performed simultaneously.By resizing and translating the video simultaneously, the attention ofthe user may be better retained on the video during the calibrationprocess.

Alternatively, resizing may follow translation or translation may followresizing.

The video may continue seamlessly throughout calibration. By continuingthe video seamlessly throughout the entire calibration process, theattention of the user may be better retained. Changing the content ofthe video part way through the calibration process may risk losing theattention of the user.

Alternatively, the video may be changed part-way through the calibrationprocess. Although this may interrupt the ongoing attention of the user,utilising new content in the video may renew the user's interest in thevideo and therefore may assist with calibration of multiple calibrationpoints. In this case, it may still be desirable to provide a consistentstream of video content for each calibration point.

It may be desirable to avoid changing the content of the video whilstthe video has the attention of the user. Therefore, changing of thevideo may only occur when it has been determined, automatically ormanually, that the attention of the user is not on the video.

The content of the video may be forced to change if it is determinedthat the attention of the user has been lost. By changing the content,attention of the user may be re-captured. Detection of attention lossmay be by detecting the general gaze direction of the user, e.g. bydetecting that they have turned their head away from the display or areclearly looking to the side of the display, and may be automatic ordetermined by an operator of the system.

The video may be accompanied by audio content. The audio content may becorrelated to the video, e.g. the audio may be noises related to theactivity shown visually on the display. By using audio and video, theuser's attention may be better retained.

The processor may be configured to repeat steps (a) to (c) forcalibration positions where it is determined that previously capturedcalibration data is inaccurate or not sufficient.

Repetition of calibration points may improve the overall calibrationprocess by removing erroneous calibration data and replacing it withaccurate calibration data.

An operator may determine that the calibration data is inaccurate or notsufficient. Oversight by an operator can make sure that the calibrationdata is good enough for future eye tracking procedures. For example, ifan operator notices that the calibration data for a particularcalibration point is inaccurate or is not sufficient, they may manuallytrigger calibration data for that calibration point to be recollected.

An automated process may determine that the calibration data isinaccurate or not sufficient. The automated process may be executed bythe processor of the system or by an external, optionally remote,processor.

The eye tracking system may further comprise a separate display forreviewing calibration data during the calibration process.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments will now be described in detail with reference tothe accompanying drawings, in which:

FIG. 1 is a representative view of a user using an embodiment of the eyetracking system of the second aspect;

FIG. 2 is a flow chart of an embodiment of the method of calibration thefirst aspect; and

FIGS. 3a to 3h are visual representations of the method of calibrationof the first aspect;

FIG. 4 is a representative view of a user using another embodiment ofthe eye tracking system of the second aspect;

FIG. 5 is a flow chart of another embodiment of the method ofcalibration of the first aspect.

DETAILED DESCRIPTION

Referring firstly to FIG. 1, there is depicted an eye tracking system100. The eye tracking system 100 is usable to track the gaze of a user102, here a non-human primate, relative to a display 104. By trackingthe gaze of the user 102 relative to the display 104, it can bedetermined where the user 102 is directing their attention when lookingat the display 104. This can be useful for many circumstances, includingas a control input for a computer, for research purposes, or fordiagnosis of medical conditions, for example.

The eye tracking system 100 comprises a display 104, on which an imagecan be presented to the user 102, and an eye tracking device 106comprising an image sensor 108 that is directed towards the user 102. Aprocessor 110 interlinks the eye tracking device 106 and the display104, enabling the processor 110 to communicate with the eye trackingdevice 106 and to send commands to the display and thus allowingcorrelation to be made between the image shown on the display 104 andthe image captured by the eye tracking device 106. By imaging the eyes,and optionally also the head position of the user 102, the eye trackingsystem 100 can determine the gaze direction of the user 102. This is awell-known process and will not be described in more detail here.

In the depicted system, the display 104 is paired with an eye trackingdevice 106 comprising the image sensor 108 and three illuminators112,114. One illuminator 112 is positioned close to the image sensor 108and can therefore be used to provide a bright pupil, or BP, image. Theother two illuminators 114 are positioned away from the image sensor 108and can be used to provide a dark pupil, or DP, image. The use of BP andDP images in eye tracking are well-known and will not be describedfurther. The eye tracking device 106 may be, for example, a Tobii EyeTracker S or a Tobii Pro Fusion, as produced by Tobii AB of Danderyd,Sweden. Depending on the particular eye tracking device used, there maybe different numbers and positions of illuminators and image sensors.The depicted embodiment is just a non-limiting example of these and thefull spectrum of arrangements will be known to the skilled person.

In order to provide good accuracy for eye tracking of a user, the eyetracking system 100 must be calibrated. The eye tracking processincreases accuracy by correlating a direction of gaze detected by theeye tracking device 106 with an image viewable at a specific point onthe display 104, known as a calibration point or calibration position.Calibration data can be collected that correlates the gaze directionwith each calibration position. In general, the more calibrationpositions that are used during the calibration process, the better theeye tracking system 100 can be calibrated for a specific user 102. Oncecalibrated, the eye tracking device 106 can be used as normal.

The present calibration process is designed to ease calibration for allusers, no matter whether they are capable of correctly understanding orresponding to instructions of an operator of the eye tracking system.The calibration process is described with reference to the eye trackingsystem 100 of FIG. 1 and the flow-chart of FIG. 2. FIGS. 3a to 3h showhow the image presented on the display 104 changes over the course ofthe calibration process.

In a first step, a video 116 is shown on the display. As in FIG. 3a ,the video 116 takes up a large proportion of the display 104.Preferably, this large proportion is the majority of the display 104. Byusing a video 116 rather than a still image, the attention of the user102 may be drawn to and may remain drawn to the display 104 over aprolonged period of time. Any type of video 116 may be shown on thedisplay 104 but it may be desirable to tailor the content of the video116 to the particular user. For example, a cartoon may be shown to smallchildren, or a video of food or animals of the same or a differentspecies may be used with non-human primates such as apes or chimpanzees.Where the content of a video is to be used for further study using theeye tracking device, it may be desirable to calibrate the device using avideo with different content to that of the study.

The video 116 is shown S100 before any sort of calibration data iscaptured and is there to capture the attention of the user 102. Once theuser's attention has been successfully captured, the rest of the rest ofthe calibration process may begin.

After initiation of the next stage of the process, the video 116 beginsto resize and translate S102 on the display 104. This allows theattention of the user 102, and thus their direction of gaze, to be drawnto a desired position of the display 104. Importantly, the video 116shown on the display 104 does not change between its action in grabbingthe attention of the user 102 and its action in calibration, i.e. thevideo content continues to play. Thus, the user 102 need not be awarethat calibration is being carried out. As shown in FIGS. 3b and 3c , thevideo 116 shrinks as it moves to the top left corner of the display,where it reaches its minimal size and ceases movement. The position atwhich the video 116 ceases movement is known as a calibration point orcalibration position, and this is predetermined by the system orpre-programmed by an operator, as is well-known in the art. It isbeneficial for the resizing and translation of the video 116 to besimultaneous, such that the gaze of the user 102 is drawn fluidly withthe transformation of the video 116. At the point at which the video 116is stationary and at its smallest size, the eye tracking device 106captures calibration data S104 to correlate the position of the gaze ofthe user 102 with the calibration position.

Because the video 116 is of a small size, it can be assured that theattention of the user 102 on the video 116 is centred on a small sectionof the display 104. Thus, the calibration of the display 104 can beprovided in the knowledge that the user 102 must be gazing at that smallsection. In addition, because the video 116 continues to play, theattention of the user 102 continues to be attracted by the video 116, instark contrast to the use of a static image, as used in previously knowncalibration techniques.

The actual size of the video when it is at its smallest can be adjusteddepending on the accuracy required by the calibration process. Theaccuracy of the calibration will be proportional to the size of thestimulus, i.e. the video, that the user is viewing. Therefore, the videocan be sized according to the accuracy that is required for the study.For example, if for the remainder of the eye tracking study it is onlyimportant to detect if the user is looking at the screen or to the leftor the right of the screen, the video may be larger in its small sizethan for a study that requires greater accuracy of the user's gaze.

Once calibration data is collected, the video 116 returns to itsoriginal size and position S106, as shown in FIG. 3d . By returning tothe original position, the attention of the user 102 may be betterretained on the video 116 than if the video 116 were to move straight toa second calibration position at another position on the display 104.

In other embodiments, it may be that the video does not return to theexact size and position that it was previously. For example, the videomay enlarge and translate but only to an intermediate size which islarger than when the video is being used to gather calibration data butis smaller than the original size. Similarly, the translation of thevideo may be away from the calibration position but not all the way backto the original position, or may be in a direction towards a subsequentcalibration position without returning first of all to the originalposition. However, the larger the video is, the more likely it is thatthe video will retain the attention of the user.

The sequence of events—resizing and translation S102, data gatheringS104, resizing and translation S106—can then be repeated for any furthercalibration positions of a calibration sequence. FIGS. 3e to 3h show thesequence for calibration with a further calibration position located inthe top right corner of the display 104. Commonly, calibration sequencesmay comprise 1, 4, 6, or 9 calibration positions, and these may bespread evenly across the display, to provide a good coverage for thecalibration. Such calibration sequences are well-known in the art.Calibration sequences having different numbers of calibration positionsmay also be provided.

As the video 116 continues throughout the calibration process, theattention of the user 102 remains drawn to the video 116, whichmaximises the chances of the calibration being accurate enough for asuccessful calibration. In other embodiments, the video content beingdisplayed may change between calibration positions. It is most importantthat the video 116 retain the attention of the user during theshrink-and-calibrate parts of the process. After the calibration datahas been gathered for a calibration position, it is less important thatthe video retain user attention, at least until the video begins toshrink to the next calibration position. Therefore, if it is necessaryto change the video content at any time, it may be done whilst the videois growing immediately after the gathering of calibration data.

In some embodiments, it may be desirable to change the content of thevideo if it is detected that the attention of the user has been lost. Inthis case, the change of the video may be advantageous in order tore-capture user attention. In this case, it may be desirable to changethe content whilst the video is being shown in full size.

In some embodiments, it may be desirable to have operator oversight ofthe calibration process. For example, after each calibration position,or at the end of a calibration sequence, the operator may review thecalibration data in order to determine if it is good enough to providean accurate calibration. The operator 218 may therefore use a computerworkstation that is in communication with the rest of the eye trackingsystem 200, as shown in FIG. 4.

The operator 218 can monitor the calibration process during itsoperation. For example, if calibration data for a calibration positionis considered to lack accuracy or to be poor in any other way, theoperator 218 may cause this calibration position to be inserted backinto the calibration sequence, either straight away or at a later pointin the calibration process. Calibration data may be considered to bepoor, for example, if there is high variability in the gaze positionduring the gathering of the data or if there is a substantial amount ofdata missing such as through the gaze tracking device being unable totrack the gaze. Calibration data may also be considered poor if theapplication of the data to the calibration model, e.g. the eye model towhich the calibration data is being applied, leads to a residual errorafter fitting the model. In each case, thresholds may be predeterminedby the system or may be set by an operator in order to determine underwhat circumstances calibration data should be rejected or considered ofpoor quality. It may also be considered to be poor if there is evidenceof user distraction. It is possible to detect such distraction by manualinspection of the calibration or validation results, for example ingraphical form, or by reviewing the data with a trained algorithm.Methods of doing so will be known to those skilled in the art.

Of course, if the calibration data is considered to be good, the processcan continue without any operator input. Because the operator 218 has aseparate display 220 associated with their workstation, the monitoringand restructuring of the calibration process can be managed withoutinterrupting the user 202, who can remain with their attention on thevideo 216 being shown. The advantage of this arrangement is thereforethat the calibration process can continue without the knowledge orspecific cooperation of the user 202.

Although this depicted embodiment uses the manual input of an operator218 to control any re-insertion of calibration positions into acalibration sequence, this step may also be completed automatically bythe processor 210 interconnecting the display 204 and eye trackingdevice 206 or a separate or remote processor. Automatically reviewingthe calibration data ensures that the calibration process continuesuntil such a time as the calibration data is considered to be accurateand trustable for ongoing eye tracking processes.

The step of reviewing S208 the calibration data is shown in FIG. 5,sequentially after the calibration data is gathered S206. If the datacalibration is good, then gathering of data at the next calibrationposition can then be continued. Alternatively, if the calibration isbad, for example by any measure discussed previously, then thecalibration sequence may be altered S210 in order to re-do thecalibration process for the same calibration position again or to addthe poorly calibrated position to the calibration sequence. Theremaining steps—those of showing the video S200, resizing andtranslating the video S202, capturing calibration data S204, and againresizing and translating the video S206—are the same as those of FIG. 2,and are given alike reference numerals.

Of course, the calibration data may also be reviewed in its entirety atthe end of the calibration sequence and any poor calibration data maylead to the re-running of the entire calibration sequence or a subset ofcalibration positions.

Where an operator 218 is present, they may also initiate the calibrationprocess once it is deemed that the user's attention has been captured bythe video being shown on the display 204. For example, the operator 218may be able to view the feed from the image sensor 208 in order to checkwhether or not the user appears to be viewing the video, or whether theuser's attention is directed elsewhere. In other embodiments, the imagesensor 208 may be configured to detect if the user 202 appears to belooking at the video and to initiate the calibration process once it isdetermined that they are.

Although the present invention has been described with reference to adisplay and eye tracking device that are remote from the user, theinvention is not limited to such arrangements. The invention is suitablefor any application where calibration of a user respective to a displayis required. For example, the invention is also suitable forhead-mounted displays, such as in virtual reality or mixed realityheadsets.

Whilst the present invention has been discussed in relation to humansand non-human primates, the method and system disclosed may also beapplied to other animals, where it is desirable to track said animal'seyes. For example, dog cognition may be of interest and the presentlydisclosed method and system are equally applicable to use on dogs asthey are to use on humans and primates. Similarly, the present methodand system could be applied to robots such as human robots, in the eventthat their visual system is designed in a way that moving shapes andcolours enact the capture of attention in the same or a similar way asin the human visual system.

1. A method for calibrating an eye tracking device configured to track agaze point of a user on a display, the method comprising: presenting avideo on the display to a user, the video having a start size and astart position; tracking the gaze of the user, using an image sensor ofthe eye tracking device; sequentially completing, for at least onecalibration position, the steps of: (a) resizing the video to acalibration size, wherein the calibration size is smaller than the startsize, and translating the video to a calibration position; (b) recordingcalibration data, using the eye tracking device, for the user viewingthe video in the calibration position; (c) resizing the video to asecond size that is greater than the calibration size.
 2. The method ofclaim 1, wherein the method of calibration comprises a plurality ofcalibration positions, and steps (a) to (c) are repeated for eachcalibration position.
 3. The method of claim 1, wherein the second sizeis the same as the start size.
 4. The method of claim 1, wherein thestart size is a size that fills or substantially fills the display. 5.The method of claim 1, further comprising, in step (c), translating thevideo away from the calibration position.
 6. The method of claim 5,wherein the translation is in the direction of the start position, andis optionally back to the start position.
 7. The method of claim 1,wherein resizing and translation of the video is performedsimultaneously.
 8. The method of claim 1, wherein the video continuesseamlessly throughout calibration.
 9. The method of claim 1, furthercomprising repeating steps (a) to (c) for calibration positions where itis determined that previously captured calibration data is inaccurate ornot sufficient.
 10. The method claim 1, further comprising monitoringthe calibration process on a separate display, to review calibrationdata during the calibration process.
 11. An eye tracking system,comprising: a display, viewable by a user; an eye tracking device,comprising an image sensor configured to track a gaze of the user on thedisplay; and a processor, configured to present a video on the displayto the user, having a start size and a start position, and further tosequentially cause, for at least one calibration position, the steps of:(a) resizing the video to a calibration size, wherein the calibrationsize is smaller than the start size, and translate the video to acalibration position; (b) recording calibration data, using the eyetracking device, for the user viewing the video in the calibrationposition; (c) resizing the video to a second size that is greater thanthe calibration size.
 12. The eye tracking system of claim 11, whereinthe processor is configured to repeat steps (a) to (c) for a pluralityof calibration positions.
 13. The eye tracking system of claim 11,wherein the second size is the same as the start size.
 14. The eyetracking system of claim 11, wherein the start size is a size that fillsor substantially fills the display.
 15. The eye tracking system of claim11, wherein the processor is further configured to cause, in step (c),translating of the video away from the calibration position.
 16. The eyetracking system of claim 15, wherein the translation is in the directionof the start position, and is optionally back to the start position. 17.The eye tracking system of claim 11, wherein resizing and translation ofthe video is performed simultaneously.
 18. The eye tracking system ofclaim 11, wherein the video continues seamlessly throughout calibration.19. The eye tracking system of claim 11, wherein the processor isconfigured to repeat steps (a) to (c) for calibration positions where itis determined that previously captured calibration data is inaccurate ornot sufficient.
 20. The eye tracking system of claim 11, furthercomprising a separate display for reviewing calibration data during thecalibration process.